As feature sizes on DRAM devices continue to decrease, it is becoming progressively harder to maintain existing levels of memory-cell capacitance. Consequently, memory-cell capacitance is likely to decrease. This means that the sense amplifiers, which are used to amplify the signals from the memory cells, need to become more sensitive to accurately amplify the smaller signals associated with such lower memory-cell capacitances.
One problem in producing more-sensitive sense amplifiers arises from the threshold-voltage mismatch between the n-type field-effect transistors (NFETs) which are used to amplify signals in a typical sense amplifier. Within a typical sense amplifier, the amplification process starts with two cross-coupled NFETs, which are used to amplify a signal from a cell. If these two NFETs have identical threshold voltages, the sense amplifier can sense an arbitrarily small signal. However, manufacturing process variations typically cause a mismatch between the threshold voltages of these NFETs. This mismatch limits the ability of the sense amplifier to accurately sense the lower signal amplitudes associated with lower cell capacitances.